The present invention relates to an ultrasonic vehicle distance sensor and indicator. It particularly relates to an apparatus and methods for determining the location of a vehicle in a defined spaced and affording an indication to the driver of the vehicle of the location of the vehicle relative to a reference location.
As most vehicle drivers can attest, parking a vehicle in a defined space, e.g., a garage, oftentimes can be quite difficult. Most drivers have difficulty in accurately judging the distance, for example, between the front bumper of the vehicle and a rear wall of a garage. Frequently, the driver may not advance the vehicle sufficiently such that the rear of the vehicle clears the garage door. Conversely, the driver may misjudge the distance between the front bumper and the rear wall of the garage and impact the vehicle against the rear wall. With recent design changes in automotive bumpers, a forceful impact of this type can oftentimes lead to substantial damage to the bumper necessitating its repair or replacement, not to mention the damage to the rear wall of the garage.
Further, it is also desirable to locate the vehicle within the defined space a certain distance from one or more reference locations laterally of the vehicle. For example, it is desirable to locate the vehicle when parking in a garage a minimum distance from the side wall of the garage to enable the door of the vehicle to be fully opened for ingress and egress. Those distances are often inaccurately judged by the driver, resulting in damage to the side door of the vehicle when the door is opened and impacted against a side wall or other objects to the side of the vehicle.
In accordance with the present invention, there is provided a novel and improved sensing and signaling device to enable the driver of a vehicle to locate the vehicle within a defined space or envelope and indicate to the driver that the vehicle is located within such space or envelope. To accomplish this, the present invention provides a sensor, for example, an ultrasonic transducer, mounted adjacent to or within the defined space, e.g., on the rear wall of a garage, for purposes of sensing the distance the vehicle is from the sensor and providing an indication to the driver of the distance from a desired reference location, typically the sensor. While the sensor may be of a number of different types, e.g., infrared, radar, microwave, preferably an ultrasonic sensor is provided. The ultrasonic sensor when mounted, e.g., on the rear wall of the garage, transmits an ultrasonic signal toward the oncoming vehicle. The echo of the signal reflected by the vehicle is returned to a receiver section of the sensor. The returned echo, processed through appropriate circuitry, i.e., given the known speed of the signal and the time between transmittal and receipt of the echo, is used to determine the distance of the vehicle from the sensor. Shortened transmit excitation burst times are used when measuring at close ranges to reduce sensor ring time. The sensor device also remains active at all times so that there is no need for the driver to activate it manually or through other contrived means such as flashing the headlights of the vehicle.
An output signal as a function of the distance to the vehicle can be used to provide visual and audible indications to the driver of the vehicle regarding the progress of the vehicle toward the sensor. For example, a series of lights may be provided on the sensor indicating predetermined distances of the vehicle from the sensor or a reference location. Thus, when the vehicle enters the preferred position within the defined space, a light, for example, a red light, may be actuated by the receiving section of the sensor to indicate to the driver that the vehicle is properly located, e.g., vis-a-vis its distance from the rear wall of the garage. Similar sensing units can be provided along one or both of the opposite sides of the vehicle. In this manner, the driver of the vehicle can position the vehicle both in the direction of motion of the vehicle and in directions perpendicular to its direction of motion within the defined space or envelope.
One inconvenient drawback common to such systems is their susceptibility to irrelevant spurious reflections from other close range off-axis or nearby stationary objects in the vicinity of the sensor. Such spurious reflections are often the cause of false detection responses that make the system unreliable or unusable in many environments--such as in a cluttered household garage where there is often found miscellaneous appliances, shelving and movable objects such as a lawnmower, gardening tools and/or other randomly placed equipment.
Although for a conventional ultrasonic transducer a seemingly narrow beam width rating or stated "acceptance angle" (typically 10.degree.) might be thought sufficient to ignore nearby off-axis object reflection artifacts, such specifications are typically indicative of transducer response measured at the "half-power" points in the beam pattern. Thus, under ordinary conditions, objects close to the sensor will be detected despite the fact that they may be considerably off axis. The present invention overcomes this problem by providing a distance dependent means for dynamically desensitizing the receiver subsystem to ignore reflection artifacts from off-axis objects close to the sensor. This is implemented by using an exponentially decaying reference signal as a detection amplitude threshold--the threshold at which a valid ultrasonic reflection is deemed present. The varying reference signal is continuously compared against the amplitude of the received ultrasonic echo signals. In this context, false responses are mitigated in the present invention by dynamically changing the detection signal amplitude threshold so as to essentially ignore reflections from close-range off-axis irrelevant objects.
In accordance with the present invention, there is provided a method of positioning a vehicle within a defined space comprising the steps of: providing an ultrasonic transducer sensor fixed at a predetermined reference location, emitting ultrasonic energy signals within the defined space and receiving echoes reflected by the vehicle while ignoring ultrasonic reflection artifacts from irrelevant off-axis objects close to the sensor, sensing the proximity of the vehicle relative to the sensor as the vehicle enters the defined space and, using the sensed proximity, indicating to a driver of the vehicle the proximity of the vehicle to the reference location--thereby enabling the driver of the vehicle to position the vehicle within the defined space. In a preferred embodiment, an improved method and apparatus for sensing the proximity of a vehicle is provided that reduces the influence of spurious reflections from irrelevant close range off-axis objects, remains active at all times without compromising power consumption, avoids false triggering due to ringing within the sensor and reduces sensor ring time during close range operation.
Accordingly, it is a primary object of the present invention to provide a novel and improved vehicle position sensor and indicating device that has a reduced sensitivity to irrelevant close range off-axis objects while enabling a driver of a vehicle to accurately and consistently locate the vehicle within a defined space or envelope.